This invention relates to rubber vulcanisates having improved physical properties.
The process of vulcanising diene rubbers by heating with sulphur and a vulcanisation accelerator has been known for many years. By this process, vulcanisates having certain physical properties, for instance tensile strength, resilience and fatigue resistance at a high level can be obtained, but such vulcanisates tend not to have good ageing properties. Apart from the addition of antioxidants which will retard oxidative heat ageing, other methods which have been proposed for making vulcanisates having improved ageing properties include the use of lower proportions of sulphur and increased proportions of accelerator relative to those which would be employed for a conventional cure, and the partial or complete replacement of sulphur by other cross-linking agents.
Vulcanisates made using such alternative systems tend, however, to lack certain of the merits of a sulphur-cured vulcanisate, and there is therefore a need for additives which will improve the ageing properties of vulcanisate while retaining the merits of using sulphur as the vulcanising agent.